定义Map时候 记得把类型写在定义的后面：在初始化时候写类型不好使

Map map = new HashMap<Integer, Integer>();
        for(int i=0;i< nums.length;i++){
            if(map.containsKey(nums[i])){
                //下一行会报错：Operator '+' cannot be applied to 'java.lang.Object', 'int'
                int newValue= map.get(nums[i])+1;//这一行会报错：Operator '+' cannot be applied to 'java.lang.Object', 'int'
                //上一行会报错：Operator '+' cannot be applied to 'java.lang.Object', 'int'
                map.put(nums[i],newValue);
            }else {
                map.put(nums[i],1);
            }
        }

正确写法：

Map<Integer, Integer> map = new HashMap<Integer, Integer>();
        for(int i=0;i< nums.length;i++){
            if(map.containsKey(nums[i])){
                int newValue= map.get(nums[i])+1;
                map.put(nums[i],newValue);
            }else {
                map.put(nums[i],1);
            }
        }